1,704 research outputs found
Energy Efficiency and Asymptotic Performance Evaluation of Beamforming Structures in Doubly Massive MIMO mmWave Systems
Future cellular systems based on the use of millimeter waves will heavily
rely on the use of antenna arrays both at the transmitter and at the receiver.
For complexity reasons and energy consumption issues, fully digital precoding
and postcoding structures may turn out to be unfeasible, and thus suboptimal
structures, making use of simplified hardware and a limited number of RF
chains, have been investigated. This paper considers and makes a comparative
assessment, both from a spectral efficiency and energy efficiency point of
view, of several suboptimal precoding and postcoding beamforming structures for
a cellular multiuser MIMO (MU-MIMO) system with large number of antennas.
Analytical formulas for the asymptotic achievable spectral efficiency and for
the global energy efficiency of several beamforming structures are derived in
the large number of antennas regime. Using the most recently available data for
the energy consumption of phase shifters and switches, we show that
fully-digital beamformers may actually achieve a larger energy efficiency than
lower-complexity solutions, as well as that low-complexity beam-steering purely
analog beamforming may in some cases represent a good performance-complexity
trade-off solution.Comment: Submitted to IEEE Transactions on Green Communications and Networkin
Massive MIMO for Next Generation Wireless Systems
Multi-user Multiple-Input Multiple-Output (MIMO) offers big advantages over
conventional point-to-point MIMO: it works with cheap single-antenna terminals,
a rich scattering environment is not required, and resource allocation is
simplified because every active terminal utilizes all of the time-frequency
bins. However, multi-user MIMO, as originally envisioned with roughly equal
numbers of service-antennas and terminals and frequency division duplex
operation, is not a scalable technology. Massive MIMO (also known as
"Large-Scale Antenna Systems", "Very Large MIMO", "Hyper MIMO", "Full-Dimension
MIMO" & "ARGOS") makes a clean break with current practice through the use of a
large excess of service-antennas over active terminals and time division duplex
operation. Extra antennas help by focusing energy into ever-smaller regions of
space to bring huge improvements in throughput and radiated energy efficiency.
Other benefits of massive MIMO include the extensive use of inexpensive
low-power components, reduced latency, simplification of the media access
control (MAC) layer, and robustness to intentional jamming. The anticipated
throughput depend on the propagation environment providing asymptotically
orthogonal channels to the terminals, but so far experiments have not disclosed
any limitations in this regard. While massive MIMO renders many traditional
research problems irrelevant, it uncovers entirely new problems that urgently
need attention: the challenge of making many low-cost low-precision components
that work effectively together, acquisition and synchronization for
newly-joined terminals, the exploitation of extra degrees of freedom provided
by the excess of service-antennas, reducing internal power consumption to
achieve total energy efficiency reductions, and finding new deployment
scenarios. This paper presents an overview of the massive MIMO concept and
contemporary research.Comment: Final manuscript, to appear in IEEE Communications Magazin
Large System Analysis of Power Normalization Techniques in Massive MIMO
Linear precoding has been widely studied in the context of Massive
multiple-input-multiple-output (MIMO) together with two common power
normalization techniques, namely, matrix normalization (MN) and vector
normalization (VN). Despite this, their effect on the performance of Massive
MIMO systems has not been thoroughly studied yet. The aim of this paper is to
fulfill this gap by using large system analysis. Considering a system model
that accounts for channel estimation, pilot contamination, arbitrary pathloss,
and per-user channel correlation, we compute tight approximations for the
signal-to-interference-plus-noise ratio and the rate of each user equipment in
the system while employing maximum ratio transmission (MRT), zero forcing (ZF),
and regularized ZF precoding under both MN and VN techniques. Such
approximations are used to analytically reveal how the choice of power
normalization affects the performance of MRT and ZF under uncorrelated fading
channels. It turns out that ZF with VN resembles a sum rate maximizer while it
provides a notion of fairness under MN. Numerical results are used to validate
the accuracy of the asymptotic analysis and to show that in Massive MIMO,
non-coherent interference and noise, rather than pilot contamination, are often
the major limiting factors of the considered precoding schemes.Comment: 12 pages, 3 figures, Accepted for publication in the IEEE
Transactions on Vehicular Technolog
Distributed Massive MIMO in Cellular Networks: Impact of Imperfect Hardware and Number of Oscillators
Distributed massive multiple-input multiple-output (MIMO) combines the array
gain of coherent MIMO processing with the proximity gains of distributed
antenna setups. In this paper, we analyze how transceiver hardware impairments
affect the downlink with maximum ratio transmission. We derive closed-form
spectral efficiencies expressions and study their asymptotic behavior as the
number of the antennas increases. We prove a scaling law on the hardware
quality, which reveals that massive MIMO is resilient to additive distortions,
while multiplicative phase noise is a limiting factor. It is also better to
have separate oscillators at each antenna than one per BS.Comment: First published in the Proceedings of the 23rd European Signal
Processing Conference (EUSIPCO-2015) in 2015, published by EURASIP. 5 pages,
3, figure
Energy Efficiency and Sum Rate Tradeoffs for Massive MIMO Systems with Underlaid Device-to-Device Communications
In this paper, we investigate the coexistence of two technologies that have
been put forward for the fifth generation (5G) of cellular networks, namely,
network-assisted device-to-device (D2D) communications and massive MIMO
(multiple-input multiple-output). Potential benefits of both technologies are
known individually, but the tradeoffs resulting from their coexistence have not
been adequately addressed. To this end, we assume that D2D users reuse the
downlink resources of cellular networks in an underlay fashion. In addition,
multiple antennas at the BS are used in order to obtain precoding gains and
simultaneously support multiple cellular users using multiuser or massive MIMO
technique. Two metrics are considered, namely the average sum rate (ASR) and
energy efficiency (EE). We derive tractable and directly computable expressions
and study the tradeoffs between the ASR and EE as functions of the number of BS
antennas, the number of cellular users and the density of D2D users within a
given coverage area. Our results show that both the ASR and EE behave
differently in scenarios with low and high density of D2D users, and that
coexistence of underlay D2D communications and massive MIMO is mainly
beneficial in low densities of D2D users.Comment: 30 pages, 10 figures, Submitte
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